This application claims priority to an application entitled xe2x80x9cApparatus and Method for Adjusting Convergence Utilizing Spline Interpolationxe2x80x9d filed in the Korean Industrial Property Office on Aug. 21, 1999 and assigned Ser. No. 99-34763, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a projection image display device, and in particular, to an apparatus and method for adjusting convergence utilizing spline interpolation.
2. Description of the Related Art
There is an increasing demand for large size and high quality in image devices. Because it is difficult to fabricate a large image device in a direct view display scheme, a projection scheme has been introduced as a solution. Convergence is a very significant factor in determining the quality and product yield of a projection TV, especially a CRT (Cathode Ray Tube) projection TV.
The current real time digital convergence system uses a fourth-order Lagrange polynomial with 5xc3x975 seed data to achieve horizontal and vertical lines by interpolation. The reason for using the fourth-order function is that the CRT surface of a projection TV is made non-spherical to increase illumination efficiency, as shown in FIG. 1. To make smooth curvature out of the surface of the CRT, five points with brusque curvature changes are selected as seed points (a) and subjected to convergence adjustment in a fourth-order Lagrange interpolation polynomial. FIG. 1 illustrates an example of a horizontal CRT non-spherical surface and seed/non-seed data ((a)/(b)) and FIG. 2 is a point connection state diagram referred to for describing the influence of a variation in convergence data at a seed point (c) on convergence data at other seed points. FIG. 3 is an exemplary graph obtained by a Lagrange interpolation and FIG. 4 is a graph showing variations in convergence data at other seed points caused by the variation of convergence data at one specific seed point in Lagrange interpolation.
One of the benefits of using the fourth-order Lagrange interpolation polynomial is that density modulation does not occur at seed points 3, 6, 9, 12, and 15 in FIG. 1. Another benefit is that a look-up table is utilized instead of complicated hardware in calculating coefficients of the Lagrange polynomial, thereby facilitating simplification of hardware and enabling real time processing.
However, the fourth-order Lagrange interpolation polynomial has the distinctive drawback that adjustment of convergence data at one seed point influences convergence data at other seed points. For example, if convergence data at point 9 on a first horizontal line is adjusted to (c), convergence data at its adjacent points are also changed in FIG. 2. While one line only is shown to be influenced in FIG. 2, all data in horizontal and vertical lines are changed at worst and, as a result, the whole image may be changed. Furthermore, density modulation may take place at end seed points 3 and 15 due to external points 1, 2, an obtained by piecewise linear interpolation in the horizontal direction instead of Lagrange interpolation.
In a general fourth-order Lagrange interpolation polynomial-using system, adjustment of convergence data at one point leads to a change in convergence data at other points, as shown in FIGS. 3 and 4. Therefore, a multi-step operation is required for convergence adjustment.
It is, therefore, an object of the present invention to provide a convergence adjustment apparatus and method which can solve the above-described problems encountered in using a fourth-order Lagrange interpolation polynomial, by use of cubic spline interpolation.
It is another object of the present invention to provide a convergence adjustment apparatus and method in which cubic spline interpolation is used in multiple steps in order to facilitate convergence adjustment.
It is a further object of the present invention to provide a convergence adjustment apparatus and method in which convergence at an intended adjustment point is efficiently adjusted and continuity between the adjusted point and its adjacent point is maintained as well.
The above objects can be achieved by providing a convergence adjusting apparatus and method using spline interpolation in a projection image display device. In the convergence adjusting apparatus, a controller calculates the unknown coefficients of a cubic spline interpolation polynomial for each line segment separated by adjustment points on a horizontal or vertical line to interpolate between the adjustment points, a memory temporarily stores the unknown coefficients, a coordinate position generator counts horizontal sync signal pulses and calculates the square and cube of the count value, a plurality of multipliers multiply the count value, the square, and the cube by the unknown coefficients received from the memory, respectively, and an adder adds convergence adjustment point data received from the memory and the outputs of the multipliers and outputs interpolation values.